Haptic devices form specific man-machine interfaces. A haptic device provides, on the one hand, control and, on the other hand, tactile sensation to interaction with a technical system. A haptic device provides its user with force-feedback information on the motion and/or force input generated by the user.
Applications, for which haptic devices may be used, include robotics, tele-operation, minimal invasive surgery, simulators and computer-based games.
A characteristic of a haptic device is its force rendering capabilities when a virtual contact with a hard body is simulated. To this end, haptic devices including parallel kinematics structures, for example a so-called Delta parallel kinematics structure, are well suited. The parallel kinematics design provides for high mechanical stiffness and low mass/inertia and, thus, high static and dynamic stiffness as well as high force levels. Such haptic devices may be used, for example, as robot or manipulator for performing programmed tasks or as a haptic device where force constraints can be applied into the hands of the operator.
Another characteristic of a haptic device is transparency. Haptic transparency is a performance criteria used to quantify the fidelity with which virtual object properties are presented to and perceived by the human user through a haptic device when the user's hand is in contact therewith.
Also, human factors are parameters to be considered in designing haptic devices, particularly with respect to components for direct contact with a user. Such components include so-called grippers. Grippers can be considered as—from users' point of view—the “handle” or “grip” of a haptic device for manual operation thereof. Grippers are usually coupled with local end-effectors of haptic devices.
Known grippers allow single point contact (e.g. by means of single finger tip) interaction with a simulated or remote environment. For manipulations, rather simple gripper designs may be used, such as pen-like and sphere-shaped structures. For multiple point interaction, which greatly enhances manipulation capabilities of the user, more complex gripper designs are required.
In, for example, virtual environment applications, an object can be grasped through the use of a virtual hand or grasping tool, which can be controlled by manipulating a gripper of a haptic device.
Human dexterity in manipulating objects is greatly determined by grasping possibility, sensual sensations and haptic feedback between different parts of a user's hand, for example thumb and fingers. To this end, so-called active or actuated grippers are envisaged (in the following, the term “active gripper” will be used). The term “active” indicates that a gripper may generate (display) forces and/or torques towards a user, for example, to provide force feedback, haptic information and the like.
Known grippers may display forces and/or torques generated passively (e.g. by means of a spring releasing energy previously input by a user), generated discretely (e.g. bi-stable components providing two distinct states [pushed vs. release] to display a short stroke possible with a tactile “click”), generated in general linear manner (e.g. a longer stroke with smooth force variation) and generated in virtually any degree of freedom (e.g. by an actuator).
Drawbacks of known active gripper include workspace requirements, bulkiness, high weight, complex design and insufficient (unrealistic) display of forces and/or torques towards users.